The fetus in the womb is surrounded by two adjacent amniotic membranes - much like the thin membrane under the shell of a chicken egg. As long as the membranes are intact, they protect the fetus by preventing bacteria from entering the uterus and amniotic fluid from leaking out.
The two membranes are called the chorion (choroid) and the amnion (aqueous membrane). Korion is the outermost layer and amnion the one closest to the fetus and adjacent to the amniotic fluid.
The fetal membranes help to protect the fetus and the umbilical cord by keeping the pressure of the amniotic fluid evenly distributed inside the uterus, for example during contractions. By allowing the fetus to move in the amniotic fluid, it contributes to the development of the fetal muscles, bones and lungs.
At the beginning of the pregnancy, the amniotic fluid is completely clear, but becomes increasingly cloudy due to hairs, sebum and skin particles shed by the fetus. Throughout pregnancy, new amniotic fluid is constantly being formed. The fetus swallows amniotic fluid, which is then absorbed in the gastrointestinal tract. The amniotic fluid is then discharged via the umbilical cord and placenta into the pregnant woman's bloodstream, but the fetus also urinates out any residual amniotic fluid. At around 38-39 weeks, the amniotic fluid volume peaks at around 1000 ml, and then declines normally. Amniotic fluid volume can be measured by ultrasound.
In the umbilical cord there are two arteries and a vein that help to supplying the fetus with oxygen-rich blood and removing carbon dioxide and waste products. The vessels are surrounded by a jelly-like structure made up of connective tissue. The umbilical cord is surrounded by the aqueous membrane and attaches to the placenta. The umbilical cord normally attaches centrally to the placenta.